This invention relates to the field of screen printing and, more particularly, to a fully automatic screen printing press operated entirely by mechanical means.
One known type of stencil screen printing device comprises a combined electro-mechanical system. Such prior art devices are sometimes referred to as flat bed printers and generally comprise a press head pivotally mounted on a fixed frame which supports a printing bed and press drive means. A printing screen is removably attached to a chase mounted beneath the press head in a position over the stock placed on the bed for printing. Mounted for reciprocal movement on the press head is a carriage assembly having a flood and squeegee bar which reciprocate across the screen during the printing cycle. Printing of stock is accomplished by lowering the carriage assembly over the stock on the printing bed, and reciprocating the squeegee across the screen to force ink therethrough to the stock.
In some of the more sophisticated versions of flat bed printers, an automatic infeed and takeoff means may be provided which acts in cooperation with the carriage assembly and press head to simultaneously place new stock on the bed for printing after removing printed stock from the bed. It is apparent that the infeed and takeoff operation and the printing cycle must act in a timed relation with one another to avoid incomplete printing of stock and possible damage to the press.
One of the more frequent problems encountered in known types of presses is the loss of synchronization between the infeed and takeoff mechanism and the press head. Normally, the infeed and takeoff operation is activated by microswitches, while the press head movement and the reciprocation of the carriage assembly are controlled by mechanical means. If an electrical failure occurred and the mechanical operation continued, the infeed apparatus could be located on the press bed as the press head makes its downward stroke, resulting in damage to the parts. To overcome this problem, redundant circuits or failsafe types of mechanisms have been proposed, but for one reason or another such systems have not proven entirely satisfactory.